Incident Light Source Research Articles

Coherent Lensless imaging with Ultra-Broadband Light Sources

We demonstrate a method for efficient lensless imaging using ultra-broadband light sources. By using a pair of time-delayed, coherent pulses in a Fourier-transform scheme, spectrally resolved diffraction patterns are obtained throughout the entire spectrum of the incident light source. We perform a proof-of-principle experiment using an octave-spanning visible light source, and obtain images of a holographic test sample with near-diffraction limited resolution. Our approach provides a promising route towards efficient high-resolution imaging using table-top high-harmonic soft-X-ray sources.

A calibration‐free, one‐step method for quantitative photoacoustic tomography

Recently reported quantitative photoacoustic tomography (PAT) has significantly expanded the utilities of PAT because it allows for recovery of tissue optical absorption coefficient which directly correlates with tissue physiological information. However, the recovery of optical absorption coefficient by the existing quantitative PAT approaches strongly depends on the accuracy of absorbed energy density distribution, and on the knowledge of accurate strength and distribution of incident light source. The purpose of this study is to develop a new algorithm for the reconstruction of optical absorption coefficient that does not depend on these initial parameters. Here the authors propose a novel one-step reconstruction approach that can directly recover optical absorption coefficient from photoacoustic measurements along boundary domain. The authors validate the method using simulation and phantom experiments. The authors have demonstrated experimental evidence that it is possible to directly recover optical absorption coefficient maps using boundary photoacoustic measurements coupled with the photon diffusion equation in just one step. The authors found that the method described is able to quantitatively reconstruct absorbing objects with different sizes and optical contrast levels. Compared to the authors' previous two-step methods, the reconstruction results obtained here show that the one-step scheme can significantly improve the accuracy of absorption coefficient recovery.

Width-to-thickness ratio dependence on photoplastic effect of ZnS nanobelt

Photoplastic effect (PPE) of individual ZnS nanobelt with different width-to-thickness (w/t) ratios was investigated by using a nanoindenter in conjunction with an incident ultraviolet light source system. The results show that the positive and negative PPEs are observed for the w/t ratios 4.9–9.6 and 3.2–4.1. At the peak indentation loads 20–50 μN, the positive and negative PPEs occur for the w/t ratios 4.9 and 3.2, however, they disappear at 60 μN. PPE is determined by w/t ratio not peak indentation load, and it is interpreted by the competing mechanisms of increase of Peierls barrier and radiation enhanced dislocation glide.

Experiment Research of Diffuse Optical Tomography Imaging in Homogeneous Medium

Given the time-domain measurement of picoseconds pulses and frequency-domain measurement of high-frequency modulation have limitations to realize, this paper introduces the experiment research which use square-wave modulation laser source as incident light source of the diffusion optical tomography in homogeneous medium. Based on the finite-element method, the forward model can be established. The analytical solution of the homogeneous medium can obtained from the derivation of the diffusion equation, after that, we build the optical experiment platform, derive the experimental solution from the platform. Finally, the consistent result is obtained by the comparison of the simulation, the analytical solution and the experimental solution. The result clearly demonstrated the accuracy and effectiveness of the proposed method which use square-wave modulation laser source as incident light source to measure the light intensity.

Skew ray tracing and sensitivity analysis of hyperboloid optical boundary surfaces

One of the most popular mathematical tools in fields of robotics, mechanisms and computer graphics is the 4×4 homogeneous transformation matrix. Our group's previous application of the homogeneous transformation matrix to flat and spherical optical boundaries has been extended to hyperboloid surfaces for: (1) skew ray tracing to determine the paths of reflected/refracted skew rays; (2) sensitivity analysis for direct mathematical expression of differential changes of incident points and reflected/refracted vectors with respect to changes in incident light sources and boundary geometric parameters; (3) a sensitivity analysis-based merit function derived directly from mathematical expression of catadioptric imaging system components. The presented methodology is highly suited to digital implementation and offers direct and rapid analytical statement of ray path, chief ray, marginal rays and merit functions of optical systems.

Epi-fluorescence microscopy.

Epi-fluorescence microscopy is available in most life sciences research laboratories, and when optimized can be a central laboratory tool. In this chapter, the epi-fluorescence light path is introduced and the various components are discussed in detail. Recommendations are made for incident lamp light sources, excitation and emission filters, dichroic mirrors, objective lenses, and charge-coupled device (CCD) cameras in order to obtain the most sensitive epi-fluorescence microscope. The even illumination of metal-halide lamps combined with new "hard" coated filters and mirrors, a high resolution monochrome CCD camera, and a high NA objective lens are all recommended for high resolution and high sensitivity fluorescence imaging. Recommendations are also made for multicolor imaging with the use of monochrome cameras, motorized filter turrets, individual filter cubes, and corresponding dyes being the best choice for sensitive, high resolution multicolor imaging. Images should be collected using Nyquist sampling and images should be corrected for background intensity contributions and nonuniform illumination across the field of view. Photostable fluorescent probes and proteins that absorb a lot of light (i.e., high extinction co-efficients) and generate a lot of fluorescence signal (i.e., high quantum yields) are optimal. A neuronal immune-fluorescence labeling protocol is also presented. Finally, in order to maximize the utility of sensitive wide-field microscopes and generate the highest resolution images with high signal-to-noise, advice for combining wide-field epi-fluorescence imaging with restorative image deconvolution is presented.

Transmission and Distribution of Optical Field in Prism Coupler

Transmission and distribution characteristics of optical field in prism coupler are studies, and the phase matching function of prism coupler is deduced based on coupled wave theory. It is shown that the stable light field distribution and mode pattern are determined by its own geometric and dielectric parameters, but have nothing to do with the categories of incident light sources. It is also found that the coupling effect would generate between waveguides through evanescent field. Our numerical simulation is based on the finite difference time domain method with perfectly matched layer absorbing boundary condition. The simulation program is compiled in MATLAB. The simulation results are analyzed carefully.

A numerical analysis method for evaluating rod lenses using the Monte Carlo method

We propose a numerical analysis method for evaluating GRIN lenses using the Monte Carlo method. Actual measurements of the modulation transfer function (MTF) of a GRIN lens using this method closely match those made by conventional methods. Experimentally, the MTF is measured using a square wave chart, and is then calculated based on the distribution of output strength on the chart. In contrast, the general method using computers evaluates the MTF based on a spot diagram made by an incident point light source. However the results differ greatly from those from experiments. We therefore developed an evaluation method similar to the experimental system based on the Monte Carlo method and verified that it more closely matches the experimental results than the conventional method.

A new palm-sized surface plasmon resonance (SPR) biosensor based on modulation of a light source by a rotating mirror

A novel surface plasmon resonance (SPR) sensing scheme was devised to develop a palm-sized SPR biosensor device. In this system, the beam from a diode laser (as the incident light source) is modulated using a rotating mirror. The reflected light from the gold chip is then captured using a CMOS image sensor, controlled by a notebook PC via a USB interface. This provides a portable POCT SPR sensor device which enables label-free and real-time analyses. This method can also eliminate the deterioration in image quality of the reflected laser light, originating from the coherency of the laser source. The sensing response of the system to the bulk refractive index was calibrated using various concentrations of glycerol solution. As a result, the SPR sensor was able to detect a ∼2.5 × 10 −6 RIU change in the refractive index of the solution without implementing any of data processing techniques. The performance of the sensor was tested by monitoring the binding of PSA to its antibody in real-time to verify its potential applicability in analyzing biomolecular interactions. The results obtained from a series of tests confirmed the practicality of the sensor for the on-site detection of a variety of substances in biology, diagnosis, the environment, and defense.

Porous Silicon Interferometric Sensors for the Detection of NerveAgent Mimics Using Various Light Sources

Various detection methods using nanostructured materials, such as distributed Bragg reflectors (DBRs), for sensing G-type nerve agent mimics have been developed. For DBRs, the versatile porous silicon (PSi) is prepared by electrochemical etching through applied square current waveform. The manufactured DBR exhibits unique optical properties providing the reflection of a specific wavelength in the optical reflectivity spectrum. The detection methods involve the shift of DBR in the reflectivity spectra under exposure to vapors of nerve agent mimics. Rapid detection has been achieved within 5 sec, in situ, and has been observed through the red-shift of the reflection peak caused by an increase in the refractive indices in PSi. Real-time detection for the nerve agent gases indicates that the measurement is reversible. The detection efficiency for nerve agent mimics is also increased when a light-emitting diode (LED, λem = 520 nm) or laser (λem = 530 nm) is used as an incident light source instead of a tungsten-halogen lamp.

Confocal white light reflection imaging for characterization of metal nanostructures

A simple far-field confocal white light reflection imaging system was proposed using a xenon (Xe) lamp as the incident light source. The best spatial resolution was determined to be about 410nm. Localized surface plasmons (LSPs) of isolated single and dimer gold nanospheres were studied and the resonance energy difference between their LSPs was extracted. Polarization dependent reflection imaging and contrast spectrum of single silver nanowires were also investigated, which correlate closely with the polarization dependent excitation of their LSP.

Simple scanner-based image analysis for corrosion testing: Concrete application

A methodology for the assessment of the crown corrosion in concrete sewer pipes was developed based upon the principle that the surface roughness increases when concrete corrodes. The roughness was quantified by correlating the depths of the surface pits to the lengths of shadows produced in a single source of incident light. A computer program was used to reconstruct a pseudo three-dimensional concrete exterior and obtain the averaged corrosion rate.

A Novel Near-field Raman and White Light Imaging System for Nano Photonic and Plasmonic Studies

AbstractWe show the approaches in achieving high resolution Raman and white light imaging. In Raman imaging, a dielectric microsphere is trapped by the incoming laser, which was focused onto the sample by the microsphere. The microsphere was also used to collect the scattered Raman signals. We show the capability of this method in imaging various types of samples, such as Si devices and gold nanopattern. This method is comparatively easier to perform, better repeatability, and stronger signal than the normal near-field Raman techniques. Besides the Raman imaging, we also show a far-field confocal white light reflection imaging system that can be used for the fast imaging and characterization of nanostructures. This system uses a xenon (Xe) lamp as the incident light source and tunable aperture to enhance the spatial resolution. It has a spatial resolution of around 370 nm at a wavelength of 590 nm. With our system, we can clearly resolve images of 300 nm nanoparticles arranged in 2D honeycomb arrays with a period of 500 nm. Localized surface plasmons (LSPs) of isolated single and dimer gold nanospheres were also studied and the resonance energy difference between their LSPs was extracted.

A new reconstructing algorithm for removing polarization effect of incident X-ray source and twin images in X-ray fluorescence holography

This paper discusses the influence of the polarization of incident X-vay on the reconstructed atomic image by numerical simulation and reconstruction, using a crystalstructure composed of 27 Fe atoms arranged in a cubic lattice as the model. Calculated results show that the choice of polarization is crucial for the atom observability. This paper proposes a new reconstructing algorithm which can eliminate the polarization effect of incident X-ray source and twin images inherent to holography at the same time. Numerical simulation and reconstruction results show that the reconstructing algorithm is effective and can be used to eliminate the influence of polarization of incident light source and twin image in experiments.

Skew ray tracing and sensitivity analysis of ellipsoidal optical boundary surfaces

The 4 × 4 homogeneous transformation matrix is one of the most commonly applied mathematical tools in the fields of robotics, mechanisms and computer graphics. Here we extend further this mathematical tool to geometrical optics by addressing the following two topics: (1) skew ray tracing to determine the paths of reflected/refracted skew rays crossing ellipsoidal boundary surfaces; and (2) sensitivity analysis to determine via direct mathematical analysis the differential changes of the incident point and the reflected/refracted vector with respect to changes in the incident light source. The proposed ray tracing and sensitivity analysis are projected as the nucleus of other geometrical optical computations.

Detection of organophosphates based on surface-modified DBR porous silicon using LED light

Organophosphonate nerve agents have been detected with DBR PSi samples containing a copper (II) sulfate. The detection efficiency is increased when a LED is used as an incident light source. DBR porous silicon containing copper (II) sulfate shows a TEP detection limit of about 150 ppb for 1 min, when a LED (λem=590 nm) is used as an incident light source.

All-fiber acousto-optic polarization monitor

We describe the operational principle of and experimentally demonstrate a narrowband, wavelength-tunable polarization monitor based on a fiber acousto-optic tunable filter. Two orthogonally vibrating acoustic waves are used to create a variable polarizer that can be used to measure the state of polarization of an incident narrowband light source. The accuracy of the polarization monitor is measured at two different wavelengths in reference to a commercial polarimeter and is shown to be within 5%.

A Measurement Method for Birefringent Plate using Elliptically Polarized Light

Abstract: The principal axis ψ and total relative phase retardation ρtot of a birefringent plate are obtained automatically using an elliptically polarized incident light source and a phase unwrapping technique. The technique overcomes the error associated with the quarter‐wave plate by making use of incident light of different wavelengths, and the unwrapping technique allows ψ and ρtot to be determined using an arctangent function without interpolation or construction of a calibration table. The proposed method is validated analytically and experimentally for a circular disk under diametral compressive load.

Process Reengineering of Collaborative Mold Design and Manufacturing – A System Engineering Evaluation Approach

One of the most popular mathematical tools in fields of robotics, mechanisms and computer graphics is the 4x4 homogeneous transformation matrix. In previous work we applied this matrix to the optical domains of flat and spherical surfaces for: (1) skew ray tracing to determine the paths of skew rays being reflected/refracted; (2) sensitivity analysis to determine by direct mathematical analysis the differential change of incident point and reflected/refracted vector with respect to change in incident light source. The present work extends our previous work to include the case of parabaloidal boundary surfaces.

Skew Ray Tracing and Sensitivity Analysis of Paraboloidal Optical Boundary Surfaces

One of the most popular mathematical tools in fields of robotics, mechanisms and computer graphics is the 4x4 homogeneous transformation matrix. In previous work we applied this matrix to the optical domains of flat and spherical surfaces for: (1) skew ray tracing to determine the paths of skew rays being reflected/refracted; (2) sensitivity analysis to determine by direct mathematical analysis the differential change of incident point and reflected/refracted vector with respect to change in incident light source. The present work extends our previous work to include the case of parabaloidal boundary surfaces.